Particle detectors, such as portable detectors, may use optical methods in the detection of aerosols within fluid samples. Optical methods are useful in detecting potentially harmful aerosols, such as biological aerosols that may be present after a biological agent attack or industrial accident. Biological molecules fluoresce when excited by ultraviolet (UV) radiation. As a result, biological molecules in an aerosol sample can be optically detected by irradiating the sample with ultraviolet radiation, and observing the fluorescence response. Since differing excitation wavelengths may be used to detect different classes of biological molecules, the excitation wavelength can be chosen to detect specific classes of biological molecules such as proteins, flavinoids, and metabolite products. However, detection methods that rely upon observing the fluorescence responses are susceptible to false positives in that certain non-biological molecules produce fluorescence responses when irradiated by ultraviolet radiation that are similar to fluorescence responses of biological molecules. This makes it difficult to determine whether an aerosol is harmful or not.
Another way of determining whether an aerosol is a biological aerosol is to obtain an atomic emission from the aerosol, e.g., using laser-induced breakdown spectroscopy. The atomic emission is then detected with an optical detector. An electronic signal produced by the optical detector in response to the atomic emission is analyzed, e.g., to determine whether inorganic materials, such as calcium, sodium, potassium, magnesium, etc., that are typically found in manufactured biological agents are present. This method, when coupled to fluorescence methods, is less susceptible to false positives than fluorescence only methods. However, this method requires expensive, power-intensive lasers and complex and expensive optical systems.